Most larger construction projects usually include one critical step when multiple things have to come together at the right time and in the right way. When building an addition onto the back of my house, that step occurred when erecting the walls. In the span of a day, the three walls were framed, balanced on top of the ground anchors, squared up, and fastened together. Individually, the walls teetered and tottered in response to every gust of wind or accidental bump. Once fastened together, they provided a stable structure to hold a roof and house important plumbing and electrical runs. Scientists find a parallel scenario leading up to the Cambrian explosion—the most dramatic increase in biological complexity in life’s history.
The appearance of almost all known phyla (roughly 70 percent) in a relatively brief window (a few million years) marked the dominant and enduring presence of multicellular organisms on Earth. Such an event required a number of prerequisite conditions—such as an abundant supply of nutrients, vast regions of shallow oceans, and an adequate oxygen supply. A few weeks ago, I highlighted research that found evidence of a Himalaya-sized mountain range that formed 50 million years prior to the Cambrian explosion. Erosion of these mountains supplied an abundance of nutrients to the margins and oceans surrounding the Gondwana supercontinent.
Recent research revealed evidence for the formation of vast shallow oceans. Prior to the Cambrian event, most of the continental material was part of the Gondwana supercontinent. The remaining continental material resided in the ancestral North American landmass called Laurentia. (See the diagram in the ScienceDaily article.) Right around the Precambrian-Cambrian boundary, Laurentia finished separating from Gondwana. This separation opened up a passage between the Pacific Ocean and Iapetus—the ancestral Atlantic Ocean.1 The increase in sea levels accompanying this event resulted in oceans covering the margins of the existing continents—the very margins enriched by nutrients from eroding mountains.
Scientists analyzing ancient sediments from China, Australia, Canada, and the United States found evidence for an adequate oxygen supply. The amount of oxygen in the atmosphere affects the types of minerals and other deposits that form. Chromium serves as a sensitive tracer of oxygen levels because it assumes different oxidation states depending on the amount of oxygen present. Chromium deposits formed more than 800 million years ago (the Cambrian era started about 540 million years ago) revealed oxygen levels less than one percent of today’s value.2 In addition, research indicates that these oxygen levels were also highly variable, subject to brief, dramatic increases that quickly fell back to extremely low levels. At present, scientists do not understand the mechanism behind the shift from low, highly variable oxygen levels to more stable, much higher oxygen levels. However, the evidence does show a completed transition prior to the Cambrian era.
Ongoing research continues to provide details on how Earth went from barren, formless, hostile-to-life beginnings to an environment teeming with a great diversity and abundance of life. Those details also point to the work of a master Craftsman fashioning a habitable abode for humanity.
- Ian W. D. Dalziel, “Cambrian Transgression and Radiation Linked to an Iapetus-Pacific Oceanic Connection?,” Geology 42 (November 2014): 979–82.
- Noah J. Planavsky et al., “Low Mid-Proterozoic Atmospheric Oxygen Levels and the Delayed Rise of Animals,” Science 346 (October 31, 2014): 635–38.